<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <title>01-布局</title>
    <style>
        body {
            margin: 0;
        }

        div {
            text-align: center;
        }
        
        #header {
            height: 50px;
            background-color: #f00;
        }
        
        #main {
            background-color: #0f0;
        }
        
        #footer {
            height: 100px;
            background-color: #00f;
        }


        span {
            border: 1px solid red;
            border: 1px red;
            border: 1px;
            border: 1px red solid;
            border: red solid;
        }
    </style>
</head>
<body>

<div id="header">header</div>
<div id="main">
    main
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</div>
<div id="footer">footer</div>

</body>
</html>